1. Field of the Invention
The present invention relates generally to the construction and use of vascular catheters. More particularly, the invention relates to atherectomy catheters having means for severing atheroma at their distal ends.
Arteriosclerosis, also known as atherosclerosis, is a common human ailment arising from the deposition of fatty-like substances, referred to as atheroma or plaque, on the walls of blood vessels. Such deposits occur both in peripheral blood vessels that feed the limbs of the body and coronary blood vessels which feed the heart. When deposits accumulate in localized regions of a blood vessel, blood flow is restricted and the person's health is at serious risk.
Numerous approaches for reducing and removing such vascular deposits have been proposed, including balloon angioplasty where a balloon-tipped catheter is used to dilate a region of atheroma, atherectomy where a blade or other cutting element is used to sever and remove the atheroma, and laser angioplasty where laser energy is used to ablate at least a portion of the atheroma. Of particular interest to the present invention are atherectomy devices and methods where a cutting blade is advanced past an opening in a housing at the distal end of a vascular catheter. By positioning the housing so that at least a portion of the atheroma passes through the opening, the atheroma can be severed by advancing the cutting blade. Typically, such cutting blades are circular and are rotated and-advanced simultaneously to effect the desired cutting.
U.S. Pat. No. 4,669,469, and European patent application EPA 163 502, each illustrate exemplary atherectomy devices of the type just described, where the cutter housing is typically a rigid metal cylinder Rigid cutter housings, however, are problematic when the catheters are being used in small, tortuous blood vessels where the catheter tip must pass through curves having small radii. Moreover, difficulties have been encountered in containing the circular cutting blade within the housing. It has generally been necessary to limit the area of the opening in the housing in order to assure containment and smooth travel of the blade. Such an approach is disadvantageous, however, since it limits exposure of the blade to the atheroma and the amount of atheroma which may be severed in a single pass of the blade. While designs which provide for travel of the blade over a movable guide wire ameliorate the problem somewhat, they still require limitations on the window opening and do not provide the smoothness of travel which is desired.
To overcome the limitations inherent in the rigid housing design, the use of flexible cutter housings has been proposed. See, U.S. Pat. No. 4,781,186, describing the construction of atherectomy catheters having flexible cutter housings which may comprise a slotted metal or metal braid configuration. While the use of flexible housings provides an improvement in the ability to position the distal end of the catheter within tortuous portions of the vascular system, such flexible housings exacerbate the problems with guiding the cutting blade within the housing. In particular, the window openings in flexible cutter housings will tend to deform as the housing is flexed. To the extent the opening is widened, the risk of losing the cutter blade is substantially increased. The use of a guide wire is of no substantial benefit since it is unlikely that the curvature of the guide wire would match that in the housing. Thus, the guide wire will be unable to guide the cutting blade along the desired arc.
For these reasons, it would be desirable to provide methods and devices to facilitate the guiding of cutting blades within the distal housings of atherectomy catheters. In particular, it would be desirable to provide guide mechanisms which allow a circular cutting blade to follow the arc of a flexible housing while it is undergoing flexing stress while in use. Alternatively, it would be desirable to provide other cutting mechanisms within the distal housing which provide for severing the atheroma and which are inherently contained within the housing and which conform to bending of the flexible housings during use.
2. Description of the Background Art
U.S. Pat. Nos. 4,669,469 and 4,781,186, and European patent application EPA 163 502, the disclosures of which are incorporated herein by reference, are described above. U.S. Pat. No. 4,772,258, describes an angioplasty catheter having distal drilling head which circumscribes and is attached to a helical drive shaft. U.S. Pat. Nos. 4,653,496, and 4,745,919, each of which are incorporated herein by reference, describe helical cutting blades having sharpened tips which may be introduced into blood vessels to remove stenotic lesions.